1. Field of the Invention
The invention relates to the method defined in the preamble of claim 1 for locating a mobile station. The invention also relates to a mobile station defined in the preamble of claim 10 for locating a mobile station. In addition, the invention relates to a base station defined in the preamble of claim 13 for locating a mobile station. Furthermore, the invention relates to the arrangement defined in the preamble of claim 16 for locating a mobile station. In addition to that, the invention relates to the location service centre defined in the preamble of claim 19 for locating a mobile station.
2. Description of the Related Art
Methods for determining the position of a mobile station are known previously, which methods are based on transferring radio signals between a mobile station and a mobile station network, and the measurement and signal processing thereof. Usually the mobile station network has a central controlling device, which controls the location process and the receivers participating in it. In these methods, location is usually based on two basic arrangements:
1. The mobile station operates as a receiver, and there are several transmitters in the mobile station network. The smallest number of transmitters depends on the location method. This arrangement is known as the mobile station based setting.
2. The mobile station operates as a transmitter, and there are several receivers in the mobile station network. The smallest number of receivers depends on the location method. This arrangement is known as the network based setting.
One such location method is a method based on the measurement of the angle of arrival (AOA) of the radio transmission, which uses direction finding (DF), in which method the mobile station transmits a radio signal to at least two base stations, which examine the angle of arrival of the signal and transmit the measurement results to the location service centre. Because of the inaccuracy of the AOA measurement, instead of defining an accurate angle, a sector from which the signal comes from is defined in this method. The mobile station is situated at the intersection of the arrival sectors. Two sectors are sufficient for the determination, but if there are more, the measurement becomes more accurate. The locations of the base stations are used as the basis of comparison for locating the mobile station. Another such location method is a method based on the transition time of a radio transmission. In this method, at least three base stations send a radio signal to a mobile station on the basis of the network, and the mobile station examines the observed time difference (OTD) of arrival of the signals, and, based on the mobile station, the mobile station transmits a radio signal to at least three base transceiver stations (BTS), which examine the observed time difference of arrival (TDOA) of the signals. In the location service centre (LSC), the arrival times are used to form at least two hyperbolas, at the intersection of which the mobile station is located. Because of the inaccuracy of the arrival times, the hyperbolas are expanded as wide bands, the intersection of which limits an area and not a certain point. The location of the hyperbolas is determined in relation to the location of the base stations.
A third such locating method is based on the radio transmission delay, which method uses the transition time between the mobile station and the base station. In this method, the mobile station and the base station exchange radio signals, the times of arrival (TOA) of which are examined. The transition time must be determined between the mobile station and at least three base stations. In mobile station systems based on Time Division Multiple Access (TDMA), it is necessary to know the transition time of the radio transmission between the mobile station and the base station in order to avoid the overlapping of the time intervals. On the basis of the transition time, the distance of the mobile station from the base station is determined as a location circle in which the radius corresponds to distance and in which the central point is at the base station. There must be at least three of the location circles. The intersection of these circles is the location of the mobile station. One such TOA location method is the Timing Advance (TA) method, which is planned to be used in the GSM system. In the GSM system, as is known, the to-and-from transmission time between the mobile station and the base station is measured. From this it is possible to calculate the distance between the mobile station and the base station.
There is also a system known as Timing Advance, in which the mobile station is forced to carry out consecutive connection switchings to the neighbouring base stations for determining its location.
Other such location methods are the Satellite-based Global Positioning System (GPS), using the identity of the serving cell and measuring the intensity of the signal received.
The known network-based methods have the drawback that heavy signalling is needed between the base stations and the service centre that carries out the location determination. In this method, the mobile station operates as a transmitter, and the network provides the receivers.
A further problem in the known network-based methods is the required coordination in the network. For example, the location service centre indicates to the receiving base stations which channels they should listen to according to the mobile station to be located, or in accordance with the basic settings of the base station, certain predetermined channels are listened to. The channels are indicated by means of time and frequency information, for example. In addition, the measurement results are transferred in the network, which adds to the load on the network.
Furthermore, some known methods based on transition time, such as TA, have the problem that a two-way connection must be established from the mobile station to many base stations before the location can be determined.
In addition, the known system has the drawback that the location process is slow.
The purpose of the invention is to provide a new method for locating a mobile station and to eliminate the above mentioned drawbacks.
The method according to the invention is characterized in what is set forth in claim 1. The mobile station according to the invention is characterized in what is set forth in claim 10. The base station according to the invention is characterized in what is set forth in claim 13. The arrangement according to the invention is characterized in what is set forth in claim 16. The location service centre according to the invention is characterized in what is set forth in claim 19. Preferred embodiments of the invention are presented in the dependent claims.
The invention relates to a method for determining the location of a mobile station by means of radio signals between the mobile station and the mobile station network. In the manner according to the invention, at least one separate location channel is formed between the mobile station and the network in addition to other channels, to which location channel the radio communications related to the measurement of the location of the mobile station is concentrated. All other radio communication related to the location of the mobile station is also preferably concentrated to this channel. Other channels here mean all the known channels used between the mobile station network and the mobile station, such as the channels for ordinary communications and signalling.
In one application of the method, two location channels are formed, of which the first location channel is used for radio communications from the mobile station to the network and the second for radio communications from the network to the mobile station. These are called the Location Access CHannel (LACH) and the Location Receipt CHannel (LRCH). The location access channel resembles the Random Access CHannel (RACH) in the uplink direction of the GSM system, and the location receipt channel resembles the Access Grant CHannel (AGCH) in the downlink direction. Uplink means communications from the mobile station to the network and downlink means communications from the network to the mobile station. In the location access channel, it is possible to send a location signal from the mobile station to the mobile station network at any time without coordination, because the mobile station knows the frequency and interval used in the location access channel, e.g. in the GSM system, and the base stations constantly monitor the channel for location signals. For example, in the Broadcast Control CHannel (BCCH) of the GSM system, a cell can inform the mobile stations of the location access channel by sending information of the frequency and time interval.
In one embodiment of the method, the measurement of the differences between the times of arrival is carried out from the impulse response.
In one application of the method, the first signal burst contains the identification information of the mobile station.
In another application of the method, the identification information is the International Mobile Subscriber Identification (IMSI).
The invention also relates to a mobile station, which comprises a locating device for determining the location by means of radio signals between the mobile station and the mobile station network. According to the invention, the locating device comprises
a processor for carrying out the locating routines,
memory for saving the locating routines and the measurement results, and
a transmitter for transmitting the first signal burst.
In one embodiment of the mobile station, the locating device also comprises a receiver for receiving the acknowledgement signal.
In one embodiment of the mobile station, the receiver is used for receiving the second signal burst, and the locating device also comprises a clock for determining the time of arrival of the burst, and the locating routines include at least determining the time difference between the bursts. Here signal bursts mean bursts received from different base stations.
The invention also relates to a base station for locating the mobile station by radio signals between the mobile station and the mobile station network. According to the invention, it comprises
a processor for carrying out the locating routines,
a memory for saving the locating routines and the measurement results,
a clock for determining the time of arrival of the first burst,
an antenna for transforming the first burst into an electric signal, and
a receiver for receiving the first burst from the antenna.
In one embodiment of the base station, it also includes a transmitter and an antenna for transmitting a second burst, and the locating routines include at least the determination of the time of arrival of the burst.
In another embodiment of the base station, the antenna is a direction finding antenna for determining the direction of arrival of the first signal burst, and the locating routines include at least the direction finding of the signal bursts.
The invention also relates to an arrangement for locating a mobile station by means of radio signals between the mobile station and the mobile station network. According to the invention, the arrangement consists of a mobile station, which comprises
a processor for carrying out the locating routines,
a memory for saving the locating routines and measurement results, and
a transmitter for transmitting the first signal burst;
and of at least two or three base stations depending on the locating method, which comprise
a processor for carrying out the locating routines,
a memory for saving the locating routines and measurement results,
a clock for determining the time of arrival of the first signal burst,
an antenna for transforming the first signal burst into an electric signal,
a receiver for receiving the first signal burst from the antenna.
In one application of the arrangement, the mobile station also comprises a receiver for receiving the acknowledgement signal.
In another application of the arrangement, the receiver of the mobile station is used for receiving a second signal burst, and the mobile station also comprises a clock for determining the time of arrival of the second signal burst, and the locating routines of the processor of the mobile station include at least the determination of the time difference between the bursts, and the base stations also comprise a transmitter and an antenna for transmitting a second signal burst.
The invention also relates to a location service centre for locating the mobile station by means of radio signals between the mobile station and the mobile station network. In practice, the Location Service Center (LSC) is only a computer which performs the calculation routines, maintains data bases, such as base station coordinates, starts the location determination and gives location information to the applications. According to the invention it comprises
a processor for carrying out the locating routines, which include at least determining the location of the mobile station on the basis of burst measurement results received from the base stations,
a memory for saving the locating routines and measurement results,
a receiver for receiving measurement results in the signalling channel from base stations, and
a transmitter for transmitting commands in the signalling channel to the base stations.
The invention has the advantage that by means of a separate location channel, the need for signalling in the network between the location service centre and the base stations is reduced. The first signal burst of the location access channel sent by the mobile station is a kind of command, to which the receivers of the base stations of the mobile station network can react for measuring the necessary location information, for transmitting the measurement results to the location service centre and for sending a possible acknowledgement to the mobile station.
Two location channels provide the advantage of bi-directional interaction during the location process. With only one location channel available, it is only possible to transmit the first signal burst from the mobile station to the network with predetermined repetition for locating the mobile station.
A further advantage of the invention is the fact that with a separate location channel, it is possible to transmit long signal bursts, which contain the mobile station identification.
In addition, the invention has the advantage that when an emergency call begins, locating can be carried out quickly and automatically.